The location of singular objects or layered transitions below the surface and properties thereof in the ground are a pivotal topic in geosciences. In mountainous regions is the investigation of objects and layer transitions specifically of interest for the seasonal snowpack, primarily to reduce the threat to humans and infrastructures by natural...

The location of singular objects or layered transitions below the surface and properties thereof in the ground are a pivotal topic in geosciences. In mountainous regions is the investigation of objects and layer transitions specifically of interest for the seasonal snowpack, primarily to reduce the threat to humans and infrastructures by natural hazards. Snow avalanches are a major natural hazard causing numerous fatalities throughout the world and they are a direct consequence of snowpack conditions. The annual fatality numbers of avalanches are fairly constant for the last 30 years, while in other fields such as e.g. road traffic these numbers decreased significantly. It can be assumed that the permanent enhancements in active and passive safety systems in road traffic are the reason for the decrease in victim numbers. In the field of professional search and rescue operations or accident prevention in avalanches such as hazard forecast, enhancements of instrumentations are marginal for the last three decades. The present study describes two different assessments for the use of ground-penetrating radar (GPR) systems to improve the instrumentation for the location of buried avalanche victims and the prediction of avalanches. Consequently, it demonstrates the feasibility of radar systems for the detection of inhomogeneities in seasonal snowpacks. With regard to the improvement of current methods to search and locate buried avalanche victims, which are not equipped with a location device (e.g. avalanche beacon), the main objective is to shorten search time. The assessment of this thesis was therefore to use helicopter-borne non-invasive location methods. To simulate helicopter flights, test arrangements were designed to perform field tests from above the surface. I developed methods to measure from 6--12 m above the snow cover. To measure non-invasively, the arrangement is based on pulsed radar technology. To shorten search time and to minimize the influence of man-made error possibilities, an automatic location software was developed. The results of the field tests present the answers of the fundamental questions for an airborne location operation and enabled the development of a location algorithm. Measurements showed, that the sidewise detectable range of 3--5 m of an antenna set-up with one transmitter -- receiver pair is rather small for the given flight height of 6 to 12 m. Furthermore, the reflection amplitude of the snow surface decreases almost linearly with the flight height. Unfortunately, in wet snow avalanches a buried object in the snowpack does not appear as typical reflection pattern and is therefore not explicitly locatable. The developed software algorithm proved to be sufficient for all applied test arrangements in dry snow conditions. The algorithm is able to distinguish between buried victims in the snowpack and reflections caused by only air holes within the snow cover. Further implementations on helicopters can be achieved, based on these results, but more field tests are necessary to adapt the software to the rougher flight conditions in helicopters. Concerning the observation of stratigraphic inhomogeneities within a snowpack, this thesis showed that a record of specific snowpack conditions from beneath the snow cover is feasible with GPR. The assessment of the present work is to provide snowpack information in avalanche endangered slopes and to follow the temporal evolution of the snowpack over a whole season. Two different kinds of field measurements in dry and wet snow conditions were performed to ascertain the GPR set-up, which provides the best trade-off between penetration depth and layer resolution. On the one hand, temporally singular measurements at different locations, concerning altitude, snowpack conditions and climatic regions in the European Alps, enabled the determination of capable test arrangements. On the other hand, a temporal monitoring of the snow cover at a fixed position over several months, facilitated the record of the change of specific parameters in the snowpack. In terms of system parameters, antennas with a center frequency of about 800--900 MHz are able to penetrate and adequately record stratigraphic transitions in dry and wet snow conditions. The radar-measured snow height in dry snow using a mean wave speed value for the conversion of the two-way travel time was in a good agreement to the probed snow depth and arose in an uncertainty slightly higher than of ultrasonic sensors. In terms of snowpack parameters, the recorded signals of the various snow covers were in good agreement with the measured snow properties. For dry snow conditions, the appearance and the manner of reflections recorded in the snow cover corresponded to the size and the algebraic sign of the gradient in snow density. Moisture in the snowpack attenuates the radar signal significantly. This thesis presents encouraging results of the use of impulse radar technology for the location of inhomogeneities in seasonal snowpacks. Parts of the presented results and methodologies (e.g. the automatic location algorithm) are possibly easily adaptable in related areas of geoscientific research and could also provide advances in other, non-snow related fields. 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An increase of the spatial and temporal resolution of snowpack measurements in Alpine or Arctic regions will improve the predictability of flood and avalanche hazards and increase the spatial validity of snowpack simulation models. In the winter season 2009, we installed a ground-penetrating radar (GPR) system beneath the snowpack to measure sno...

An increase of the spatial and temporal resolution of snowpack measurements in Alpine or Arctic regions will improve the predictability of flood and avalanche hazards and increase the spatial validity of snowpack simulation models. In the winter season 2009, we installed a ground-penetrating radar (GPR) system beneath the snowpack to measure snowpack conditions above the antennas. In comparison with modulated frequency systems, GPR systems consist of a much simpler technology, are commercially available and therefore are cheaper. The radar observed the temporal alternation of the snow height over more than 2·5 months. The presented data showed that with moved antennas, it is possible to record the snow height with an uncertainty of less than 8% in comparison with the probed snow depth. Three persistent melt crusts, which formed at the snow surface and were buried by further new snow events, were used as reflecting tracers to follow the snow cover evolution and to determine the strain rates of underlaying layers between adjacent measurements. The height in two-way travel time of each layer changed over time, which is a cumulative effect of settlement and variation of wave speed in response to densification and liquid water content. The infiltration of liquid water with depth during melt processes was clearly observed during one event. All recorded reflections appeared in concordance with the physical principles (e.g. in phase structure), and one can assume that distinct density steps above a certain threshold result in reflections in the radargram. The accuracy of the used impulse radar system in determining the snow water equivalent is in good agreement with previous studies, which used continuous wave radar systems. The results of this pilot study encourage further investigations with radar measurements using the described test arrangement on a daily basis for continuous destruction-free monitoring of the snow cover. Minimize

Ground-penetrating radar systems (GPR) offer a wide field of applications.Especially in cryospheric implementations GPR proved to be an adequate toolto determine fast and non-destructively media transitions. In this study, weanalyse the feasibility of impulse radar in recording internal snowpack transitions of density or moisture content. The ut...

Ground-penetrating radar systems (GPR) offer a wide field of applications.Especially in cryospheric implementations GPR proved to be an adequate toolto determine fast and non-destructively media transitions. In this study, weanalyse the feasibility of impulse radar in recording internal snowpack transitions of density or moisture content. The utilized impulse radar systems for this research purpose are commercially available and the gathered data needs no calibration measurement for interpretation, which is a distinct advantage in comparison to frequency modulated continuous wave (FMCW) systems. Currently available methods monitoring seasonal snowpacks are either destructive as snow profiling or insufficient for measuring in slope areas or to determine snow stratigraphy as ultra-sonic sensors. Additionally, the risk exposure for the profiling teams is often a limiting factor for the data acquisition, especially in avalanche paths and ridge areas. In such regions an all-season monitoring system must be secured against being destroyed by avalanches. Thus, the implemented system operates from beneath the snowpack measuring in upward direction. The GPR system was tested in several varying snow conditions as cold dry snow and wet snowpacks. Furthermore, different frequencies, polarisations and two different radar systems were analyzed on their applicability for the snowpack monitoring from beneath and the system was utilized in periods with various meteorological parameter. The results of these preliminary tests showed, that with a moved antenna it is possible to record snow layers in dry snow with adequate density steps and layer thickness, supplementary to the snow depth. A one meter-thick wet snowpack was penetrateable although the signal was very much attenuated. GPR systems with frequencies above 1GHz provided insufficient pentration depth in late season snowpacks. Analysis of reflection phases allowed interpretation of their physical origin in terms of permittivity. The system set-up used is capable of improving information of spatial and temporal snow-pack characteristics especially in stratigraphy and snow depth and has the potential to be remotely operated. Minimize

Currently available methods monitoring seasonal snowpacks are either destructive as snow profiling or insufficient for measuring in slope areas or todetermine snow stratigraphy as ultra-sonic sensors. Internal snowpack information is indispensably necessary for the prediction of the current avalanche danger. Furthermore, in mountain regions the ...

Currently available methods monitoring seasonal snowpacks are either destructive as snow profiling or insufficient for measuring in slope areas or todetermine snow stratigraphy as ultra-sonic sensors. Internal snowpack information is indispensably necessary for the prediction of the current avalanche danger. Furthermore, in mountain regions the spatial distribution of snow accumulations by wind is extremely inhomogeneous. Even single measurements of at least the varying snow depth at ridge areas or in avalanche paths can significantly improve the predictability of avalanches. In such areas, the risk exposure for the profiling teams is often a limiting factor for the data acquisition. An observation of the snowpack development with time enables real-time information about accumulation rates and settlement speed. However, a temporal observation of the snow depth and of internal layering is only possible with sensor systems which are able to penetrate the snowpack as well as adequately resolve internal layers. Thus, in this study, the feasibility of groundpenetrating radar (GPR) systems in recording snow depth as well as internal snowpack transitions of density or moisture content was analyzed. Especially in cryospheric implementations GPR proved to be an adequate tool to determine fast and non-destructively media transitions. The utilized impulse radar systems for this research purpose are commercially available and the gathered data needs no calibration measurement for interpretation, which is a distinct advantage in comparison to frequency modulated continuous wave (FMCW) systems. In regions with a predominant avalanche danger, an all-season monitoring system must be secured against being destroyed by avalanches. Thus, the implemented system operates from beneath the snowpack measuring in upward direction. The GPR system was tested in several varying snow conditions as cold dry snow and wet snowpacks. Furthermore, different frequencies, polarizationsand two different radar systems were analyzed on their applicability for the snowpack monitoring from beneath and the system was utilized in periodswith various meteorological parameter. The results of these preliminary tests showed, that with a moved antenna it is possible to record snow layers in dry snow with adequate density steps and layer thickness, supplementary to the snow depth. A one meter-thick wet snowpack was penetrateable although the signal was very much attenuated. GPR systems with frequencies above 1 GHz provided insufficient pentration depth in late season snowpacks. Analysisof reflection phases allowed interpretation of their physical origin in terms ofpermittivity. The system set-up used is capable of improving information ofspatial and temporal snow-pack characteristics especially in stratigraphy andsnow depth and has the potential to be remotely operated. Minimize

Year of Publication:

2009

Source:

EPIC3IGS, International Symposium on Snow and Avalanches, Manali, India.

EPIC3IGS, International Symposium on Snow and Avalanches, Manali, India. Minimize